PROJECT SUMMARY A simple, safe, reliable mechanical replacement for the failing human heart would dramatically impact health care. Over the past four decades, substantial effort has been expended to develop a cardiac replacement device (CRD), but technical hurdles have been prohibitive. The introduction of the constant-flow (CF) rotary blood pump over the last 7 years has revolutionized the field of cardiac support. These pumps are smaller, more energy efficient, and less expensive to produce than their pulsatile predecessors, and their lack of valves and flexible membranes makes them impervious to mechanical wear. More than 1,000 patients have been treated with CF pumps; one of the first such pumps to be implanted functions well more than 6 years later. The goal of the proposed BRP project is to show that a next-generation CRD comprising two integrated CF (HeartMate III) rotary pumps can provide adequate pulmonary and systemic circulation to meet physiologic demands. The specific aims of this project are (1) to refine and improve the CRD for total cardiac replacement using combined engineering and in vivo experiments, such that the device allows calves to thrive for up to 3 months after implantation, and to compare the physiology of the calves using the CRD in constant-flow (pulseless) mode or actuated to impart a physiologic pulse pressure at 40 pulses/min; (2) to observe the effects of pulseless and reduced-pulse perfusion at the microvascular level in the lungs and other organs; and (3) to evaluate the exercise capacity of CRD-implanted calves and the ability of the CRD to respond to increased metabolic demands during exercise. This study should provide the necessary evidence to shift global efforts at CRD development from volume-displacement to CF technology and will hasten the day when management of end-stage heart failure can be crossed off the list of unmet clinical needs. The assemblage of pioneers in the field, innovative talent, experienced institutions, and resources proposed for this work-as well as the longstanding collaboration between the participating institutions that has culminated in pioneering clinical trials-uniquely positions this BRP team to successfully achieve its stated goals.